1. Field of the Invention
The present invention relates to a clamping device for keyless mounting of a hub to a shaft. More specifically, the invention is a device comprising a pair of wedge-shaped clamping rings positioned in the annular space between the shaft and the hub and is an improvement to the device disclosed in U.S. Pat. No. 3,501,183 to Andrew Stratienko.
2. Description of the Prior Art
A number of hub-to-shaft connecting devices exist which employ some form of clamping rings placed in the annular space between the hub and the shaft. Such devices are useful for connecting the hub to the shaft without the use of keys in either the hub or shaft. A particularly satisfactory device of this type, disclosed in the above-mentioned patent, employs a pair of nesting wedge rings. The inner wedge ring has a cylindrical inner surface for gripping the shaft, and the outer wedge ring has a cylindrical outer surface for gripping the inner surface of the hub bore. The interacting surfaces of the wedge rings are provided with matching shallow-angle annular tapers, and at least one of them is provided with a stable, dry anti-friction material, such as Teflon, preventing metal-to-metal contact between the rings.
The device includes axial force means for forcing one wedge ring into engagement with the other wedge ring, thereby contracting the inner ring tightly about the shaft and expanding the outer ring into tight engagement with the hub bore.
The wedge angle and magnitude of coefficient of friction on the ring surfaces has such interrelation as to provide a self-locking action in the rings. Self-locking results when the axial component of force exerted on one of the wedge rings by the other wedge ring when forced into engagement is less than the frictional force between the cylindrical surfaces of the wedge rings and the shaft or hub, whichever it engages, so that by increase of axial force further engagement occurs rather than the rings sliding on the smooth surfaces of the shaft or hub.
The preferred embodiment of the locking device is also self-releasing, which means that the wedge rings automatically disengage from each other when the axial force is relaxed. Self-releasing results when the radial force exerted by the contracted inner ring and the expanded outer ring on each other has an axial component of force which is large enough to disengage the wedge rings when the axial engaging force is relaxed. By proper selection of the taper angle, the anti-friction material, and the straight cylindrical surface frictional characteristics of the wedge rings, the clamping device can be designed to be both self-locking and self-releasing. Such design considerations are described in detail in the above-mentioned U.S. Pat. No. 3,501,183, which is herein incorporated by reference.
Although the axial clamping device embodiments of U.S. Pat. No. 3,501,183 are capable of producing extremely large locking forces between the hub and shaft in the axial direction, the unmodified form does not provide good rotational locking. A modified embodiment of this axial device employs a key placed in matching slots of the inner and outer wedge rings to increase the rotational locking force between the two wedge rings. But this embodiment permits only partial use of the rotational gripping capacity of the clamping device designed within practical limits of size.
The rotational gripping capacity between the inner ring and the shaft and between the outer ring and the hub are much higher than the rotational gripping capacity on the slippery surfaces between the wedge rings, even with a key placed between the rings. Since very little rotational gripping action results between the slippery tapered surfaces of the wedge rings, the key must take most of the rotational force transmitted. However, the rotational force transmitted by the key stresses the contact surfaces and body of the rings over their entire annular circumference, and since the rings are thin and have large circimferential lengths, their capacity is small and circumferential deflection is big. Their capacity can be increased by increasing the ring thickness, but it is undesireable to increase the size of the annular space between the hub bore and the shaft for a number of obvious reasons, one of which is that increasing the hub bore results in a weaker hub and limited use of the device to only the large diameter hubs.
Additional problems exist in the use of a key for a rotational stop between a pair of wedge rings. In particular, the expansion and contraction of the wedge rings results in the key slots either becoming wider than the key or closing up to grip the key so tightly that it restricts free engagement of the rings. When the key slots open up, backlash develops which prevents reversal loading or accurate "timing" applications.